Abstract

The aerodynamic interactions that can occur within a wind farm result in the constituent
turbines generating a lower power output than would be possible if each of the turbines
were operated in isolation. Tightening of the constraints on the siting of wind farms is
likely to increase the scale of the problem in the future. The aerodynamic performance of
turbine rotors and the mechanisms that couple the fluid dynamics of multiple rotors can
be understood best by simplifying the problem and considering the interaction between
only two rotors. The aerodynamic interaction between two rotors in both axial and yawed
wind conditions has been simulated using the Vorticity Transport Model. The aerodynamic
interaction is a function of the tip speed ratio, the separation between the rotors, and the
angle of yaw to the incident wind. The simulations show that the momentum deficit at a
turbine operating within the wake developed by the rotor of a second turbine can limit
substantially the mean power coefficient that can be developed by the turbine rotor. In
addition, the significant unsteadiness in the aerodynamic loading on the rotor blades that
results from the inherent asymmetry of the interaction, particularly in certain configura-
tions and wind conditions, has considerable implications for the fatigue life of the blade
structure and rotor hub. The Vorticity Transport Model enables the simulation the wake
dynamics within wind farms and the subsequent aerodynamic interaction to be evaluated
over a broad range of wind farm configurations and operating conditions.